1. Field of the Invention
The invention relates to a plenum according to the preamble of the first claim.
2. Discussion of Background
In the design of modern gas-turbine plants, economical and environmental aspects play an increasingly important role. In this connection, with regard to preserving natural resources and in particular while avoiding high emission values, attempts are made to optimize, in their energy-conversion properties, those individual components of a gas-turbine plant in which energy is converted.
In the case of gas-turbine plants, the combustion chamber, in which gas and/or liquid fuel is mixed with precompressed air and made to ignite, forms the heart of the energy conversion. In this case, the combustion of the fuel atomized in air is to be effected as completely as possible, so that all the fuel burns while developing the highest possible temperatures. On the one hand, combustion of the fuel to the fullest possible extent leads to optimum energy conversion, as a result of which the efficiency of the entire gas-turbine plant is substantially determined; on the other hand, the emission gases NO.sub.x and CO.sub.2 gases can be considerably reduced at the highest possible combustion temperatures, as a result of which a decisive, positive influence can be exerted on the environmental pollution.
In addition to the optimization of burner arrangements which produce as homogeneous a fuel atomization as possible and thus uniform combustion, it is important, in particular during the operation of modern burner arrangements as described, for example, in European Patent EP 0 321 809 B1, that the compressed air in the plenum of the burner arrangement is free of turbulence as far as possible in an undisturbed air flow and is available in a directed manner. Modern burners, as can be gathered from the publication cited above, have conical contours which provide narrow inlet slots along the outside of their cone, and the air flow required for the mixing of fuel and air has to be injected through these inlet slots.
The problems which are associated with the directing of the flow inside a plenum, into which flow an air flow is to be directed as far as possible free of turbulence in inlet openings of a burner provided in the plenum, are to be shown with reference to FIGS. 1a and 1b, which represent the prior art.
FIG. 1a shows a casing G into which gas flows 1, 2 are blown via inlet openings 4, 5. The velocity on a statistical average disappears at an impingement point A of the two gas flows 1, 2, called partial streams below. In addition, the limit flow lines of the two partial streams 1, 2 which pass through the impingement point A attain the same static pressure at this location. For these reasons, the total pressure on both limit flow lines must be the same. As a rule, the two partial streams 1, 2 experience different friction losses on their way from the compressor diffuser through the cooling system of the combustion chamber up to the air dome/plenum of the combustion chamber, since the entry velocities into the plenum 6 of the combustion chamber are not exactly the same. For this reason, the partial streams 1, 2 have different total pressures. Due to the total-pressure difference of the two partial streams 1, 2, the impingement point A of the two partial streams is forcibly displaced (as shown in FIG. 1b) into the immediate vicinity of the inlet opening of the partial stream having the smaller total pressure.
On account of the above-described flow properties which are inherent in a plurality of gas flows introduced into the interior of a casing for their mutual mixing or combining, the air supply, shown in FIG. 1b in the ideal case, to a burner 9 which is arranged inside a plenum 6 is greatly impaired.
The plenum 6 is surrounded by a casing wall G and has on the left-hand side two inlet openings 4, 5 for two gas flows 1, 2, which are directed along the casing inner wall 3 into the interior of the plenum 6. The gas flows 1, 2 coincide in a region which is located around the impingement point A and from which a common, free gas flow 7 into the interior of the plenum 6 develops. In the ideal case, the common, free gas flow 7 should enter a gap-like inlet opening 8 of the burner 9 and be mixed there with gaseous and/or liquid fuel and be made to ignite in a combustion chamber 15.
On account of the above flow effects, however, the common, free gas flow does not develop into an undisturbed, uniform flow, but is subjected to an unsteady lateral movement relative to the inlet opening 8 of the burner and in addition has very pronounced, turbulent flow portions. However, this generally leads to considerable impairment of the aerodynamic properties of the burner 9, which not least have an effect on poor combustion, as a result of which the emission values of the burner are made much worse. Likewise, flashback effects may occur in combination with turbulence effects inside the burner, which are initiated by the common, entering gas flow 7, and these flashback effects may lead to the extinction of the combustion flame or to overheating.